Wenn die Sonne scheint, werden unsere Kleider schnell trocken.

Wenn introduces a subordinate clause. In this sentence, it means when or if, depending on context.

Here it is best understood as a general condition or repeated situation:

• Wenn die Sonne scheint ... = When/If the sun is shining ...

In German, wenn is very common for:

• conditions: if
• repeated or general time situations: when

It is different from als, which is used for a single completed event in the past.

Because wenn creates a subordinate clause, and in German subordinate clauses the conjugated verb usually goes to the end.

So:

• die Sonne scheint = main clause word order
• wenn die Sonne scheint = subordinate clause, so scheint moves to the end

This is one of the most important word-order patterns in German.

Because the sentence starts with a subordinate clause:

• Wenn die Sonne scheint, ...

In German, the finite verb in the main clause must come in second position. The entire wenn clause counts as the first position, so the verb comes immediately after it:

• Wenn die Sonne scheint, werden unsere Kleider schnell trocken.

That means the subject unsere Kleider comes after the verb.

This is often called inversion, but it is just normal German verb-second word order.

Compare:

• Unsere Kleider werden schnell trocken.
• Wenn die Sonne scheint, werden unsere Kleider schnell trocken.

Werden has more than one use in German.

Here it does not mean future. It means become.

So:

• trocken werden = to become dry

That is why the sentence means that the clothes become dry quickly, not that they will dry quickly in a future-tense sense.

German often uses werden + adjective for a change of state:

• müde werden = become tired
• krank werden = become sick
• trocken werden = become dry

Because trocken is a predicate adjective here, used after werden.

Predicate adjectives in German do not take adjective endings.

Compare:

• die trockenen Kleider = the dry clothes
  
  • here the adjective comes before the noun, so it gets an ending
• Die Kleider werden trocken = the clothes become dry
  
  • here the adjective comes after the verb, so it has no ending

So trocken is correct.

It is nominative plural, because it is the subject of the main clause.

The verb werden agrees with unsere Kleider:

• unsere Kleider = our clothes
• plural subject, so the verb is werden

If it were singular, you would get:

• Unser Kleid wird schnell trocken.
  = Our dress/clothing item becomes dry quickly.

Because Kleider is plural nominative here.

Unser- behaves like a determiner and changes its ending according to case, gender, and number.

Here:

• Kleider = plural
• subject of the sentence = nominative
• so the correct form is unsere

Compare:

• unsere Kleider = our clothes (nominative/accusative plural)
• mit unseren Kleidern = with our clothes (dative plural)

Because the subject is die Sonne, which is third person singular.

So the verb scheinen is conjugated as:

• ich scheine
• du scheinst
• er/sie/es scheint
• wir scheinen
• ihr scheint
• sie/Sie scheinen

Since die Sonne = she/it grammatically singular, the correct form is scheint.

Schnell is an adverb meaning quickly. It describes how fast the clothes become dry.

So:

• werden ... trocken = become dry
• schnell = quickly

Together:

• werden schnell trocken = become dry quickly

It is modifying the whole process, not just the adjective by itself.

No, German word order is somewhat flexible, though some positions sound more natural than others.

This sentence:

• Wenn die Sonne scheint, werden unsere Kleider schnell trocken.

is completely natural.

You may also hear:

• Wenn die Sonne scheint, werden unsere Kleider trocken.
• Wenn die Sonne scheint, trocknen unsere Kleider schnell.

The chosen position with schnell before trocken sounds very natural because it keeps the idea become dry quickly together.

Yes, absolutely. That is also correct and natural.

There is a slight difference in feel:

• werden ... trocken emphasizes the resulting state: the clothes become dry
• trocknen focuses more directly on the process of drying

In everyday German, both are possible.

Because in German, a subordinate clause is normally separated from the main clause by a comma.

So after:

• Wenn die Sonne scheint,

you need the comma before the main clause begins:

• werden unsere Kleider schnell trocken.

This comma is required in standard German spelling.

Yes. Die Sonne scheint is a very common and natural expression meaning that the sun is shining.

It is often used in weather-related sentences, for example:

• Die Sonne scheint.
• Wenn die Sonne scheint, gehen wir raus.
• Heute scheint die Sonne.

So this sentence sounds very natural in everyday German.